1. Field of the Invention
The present invention relates to a copy machine provided with an original reading apparatus and at least one of the post processing functions of stapling and punching, wherein an image is formed on a recording sheet based on the image data obtained by reading an original.
2. Description of the Related Art
The copy machine employed over a wide range in an office and others includes a digital image forming apparatus for forming an image based on the image data obtained by reading original, and a post processing apparatus for stapling and punching.
Such a copy machine has an original reading apparatus that reads images on multiple numbers of originals sequentially page by page, and generates image data. The user sets an original on the original reading apparatus, sets the number of copies, stapling and punching operations and presses the Start button, whereby the set number of prints are stapled or punched, and are outputted.
In the meantime, in the duplex copying, original reading is applied sequentially to the back surface image after the front surface image. Similarly, the front surface image and back surface image formation are executed sequentially.
In such duplex copying procedure, both the original reading and image formation are performed sequentially for the front and back surface images, and this requires much time. To solve this problem, there is an active demand for a copy machine capable of simultaneously reading and printing both the front and back surface images.
An image forming apparatus capable of simultaneously printing both the front and back surface images has not yet come into widespread use because of a large size and high cost. An original reading apparatus capable of simultaneously reading the front and back surface images has been proposed and is coming into commercial use, as disclosed in the Unexamined Japanese Patent Application Publication No. 7-193680 (hereinafter referred as JPA7-193680), because a small-size and low cost version can be implemented.
Referring to FIG. 1, the following describes the copy machine as an embodiment of the present invention and the problems to be solved by the present invention.
The copy machine of FIG. 1 includes an image forming apparatus A, post processing apparatus B and sheet-through type original reading apparatus C.
The original documents D are placed on an original feed tray 21, and are fed sheet by sheet. Passing through the conveyance path, they are ejected onto the original ejection tray 22. In the conveyance path, a line image sensor 23 sequentially reads the images on the original document D from the leading end, and forms image data.
The recording sheets P are accommodated in the sheet feed tray 4, and are fed one by one from the sheet feed tray 4 to reach the image forming section 5. In the image forming section 5, an image is formed on the recording sheet P, and the formed image is fixed on the recording sheet P by the fixing apparatus 6.
In the punch mode, the recording sheets P ejected from the image forming apparatus A are punched by the puncher 10 of the post processing apparatus B and are then ejected into the ejection tray 12.
In the staple mode, the recording sheets P are stacked on the stacker 13, and the right ends of the recording sheets P are stapled by a stapler 11 installed on the right end of the stacker 13.
Referring to FIG. 2, the following describes the positional relationship between the recording sheet and image in the copying process wherein originals are read and copied, and stapling or punching operation is performed.
As shown in FIG. 2 (a), stapling or punching may be applied to the right, left and top ends of the recording sheets P. Stapling or punching will be explained in terms of post processing
It is a common practice that post processing FS1 is applied to the left end of the page, and post processing FS2 is applied to the left end top. The post processing FS3 to be applied to the top end in the case of vertical binding is not used frequently, and the post processing FS4 to be applied to the right end is rarely used.
The following describes the post processing FS1 and FS2 in FIG. 2 (a)
The original document D of FIG. 2 (b), namely, the original document D carrying the image F is read out, and an image F is formed on the recording sheets P in an inverted form as shown in FIG. 2 (c). In FIG. 2 (c), the image F is indicated by a dotted line. This means that the image is formed on the back surface of the recording sheets P.
In the staple mode, the recording sheets P are ejected from the image forming apparatus A in the down-face state wherein the image is carried on the lower surface. Then the recording sheets P are fed to the post processing apparatus B and are stacked on the stacker 13. When the recording sheets P in the set number have been stacked, the right end as the back end is stapled by the stapler 11, as shown in the post processing FSA, whereby the bundle of recording sheets P is bound.
In the punch mode, the back end of the paper is punched in the process of the recording sheets P being fed horizontally to the post processing apparatus B.
The recording sheets P having been finish-processed are stacked onto the ejection tray 12 of the post processing apparatus B face down wherein the image carrying surface faces downward.
Such post processing is inadequate because it is intended to bind the end of line in the horizontally written original.
The adequate position of post processing is indicated by the FSB of FIG. 2 (d).
Comparison between FIG. 2 (c) and FIG. 2 (d) shows that the image of FIG. 2 (d) is 180 degrees rotated with reference to that of FIG. 2 (c).
According to the conventional method, the image is rotated 180 degrees by image processing or image data processing, and the image is formed on the recording sheet P, as shown in FIG. 2 (d). Image processing wherein the image is rotated 180 degrees is called image rotation.
In the down-face state of FIG. 2 (d), the recording sheets P stacked on the ejection tray 12 are assumed as having been bound or punched at an adequate position.
Image rotation requires a large memory capacity (e.g., 8 Mbytes for A3-sized paper).
In usual copying operation, the memory is initialized at the time of image formation, and this does not cause insufficiency in the memory capacity for image rotation. In the reservation-based copying operation wherein the image data obtained by reading is stored in the memory and the image data is sequentially read out at the time of printing, whereby the image is formed, or in the copying operation to be performed simultaneously with facsimile reception, the memory is used up for other jobs, with the result that the memory capacity may be insufficient and image rotation may fail to be performed.
Thus, the user will have to wait until the termination of the reserved job, or will be forced to take a copy without performing the desired post processing.
The suspension of work due to insufficient memory capacity will be described with reference to FIG. 3.
FIG. 3 shows how the image memory is used in the reserved job, wherein the image memory capacity is assumed as 64 Mbytes.
Assume the copying job 1 wherein stapling of forty originals is designated, and the copying job 2 wherein stapling of eighty originals is designated during the execution of the job 1.
In the job 1, 8 Mbytes for image rotation and 14 Mbytes for 40 images are occupied. In the job 2, 8 Mbytes for image rotation and 28 Mbytes for 80 images are occupied
This results in 8+14+8+28=58 Mbytes being occupied for jobs 1 and 2. Thus, the free capacity is 6 Mbytes. If a job following the jobs 1 and 2 involves image rotation, reservation of this job will be disabled and the user has to wait for the termination of the jobs 1 and 2.
To avoid such a problem, the memory capacity should be increased, but this will require a cost increase, and is not to be recommended.
The present invention is intended to solve the problem resulting from the aforementioned insufficiency of memory capacity, using the duplex simultaneous reading function of the original reading apparatus disclosed in the JPA7-193680.